The proposed research will examine the immunobiological relationships between host and parasite in chronic African trypanosomiasis. Specific B lymphocyte, T lymphocyte and macrophage functions will be assessed in mice at various stages of infection. Conclusions will be made concerning 1) the nature of the host's protective immune response to the parasites 2) the level and nature of generalized immune system aberrations caused by the parasites, 3) the significance of such aberrations for the host in terms of morbidity and loss of protection to the parasites, and 4) whether immunotherapy can restore immunological responsiveness and effectively alter the balance between host and parasite in favor of the host.